This invention relates to a curable polyorganosiloxane composition and, more particularly, to a self-adherable liquid silicone elastomer composition which can be cured at a relatively lower temperature and adhered firmly to a substrate such as a metal or plastics without the use of a primer.
Liquid silicone compositions cured through an addition reaction between hydrosilyl groups and alkenyl groups bonded to silicon atoms are already well known in the art. This kind of silicone composition is excellent in heat resistance, electrical insulating ability, etc. and can be improved in mechanical strength and endowed with self-extinguishing property by including fillers such as silica. Therefore, they find many uses in potting of electrical and electronic parts, impregnation of coils, etc.
However, since this silicone composition itself has no adhesiveness, it is often restricted in its uses. Accordingly, in order to impart adhesiveness to the silicone composition, many attempts have been made to add appropriate additive components as the third component.
As the third component, there has been known to add a polysiloxane having hydrogen atoms bonded to silicon atoms and trialkoxysilylalkyl groups in combination (Japanese Provisional Patent Publication No. 16952/1973); a silane or a siloxane having an acryloxyalkyl group and an organic peroxide (Japanese Provisional Patent Publication No. 26855/1975); a polyorganohydrogensiloxane having epoxy groups and/or ester groups bonded to a silicon atom through carbon atoms in the molecule (Japanese Provisional Patent Publication No. 39345/1975); a polyorganohydrogensiloxane having a hydrogen atom bonded to a silicon atom and a 2-[3-(trialkoxysilyl)propoxycarbonyl]ethyl group or a 2-[3-(trialkoxysilyl)propoxycarbonyl]propyl group in the molecule (Japanese Provisional Patent Publication No. 48853/1979); and further a polyorganosiloxane blocked at both ends with silicon atoms bonded to one acryloxyalkyl group and two alkoxy groups (Japanese Provisional Patent Publication No. 118453/1978). However, all of these compositions involve problems such as insufficient self-bonding to various substrates to be used for electrical and electronic parts or substrates to be used for gaskets of automobile parts, or lowering in mechanical characteristics of elastomers (cured silicone elastomer compositions), etc. and therefore not satisfactory in practical application.